Investment Strategy	Feb. 28, 2026
Western Asset SMASh Series M Fund
Prospectus [Line Items]
Strategy [Heading]	Principal investment strategies
Strategy Narrative [Text Block]	Under normal circumstances, the fund expects to invest primarily in a combination of U.S. dollar denominated and non-U.S. dollar denominated investment grade (that is, rated in the Baa/BBB categories or above, or, if unrated, determined to be of comparable credit quality by the subadviser) debt obligations of U.S. and non-U.S. issuers (including emerging market issuers) and in derivatives and other instruments relating to such investments. The fund intends to invest a substantial portion of its assets in mortgage-related securities (including collateralized mortgage obligations), U.S. government securities and money market instruments. The fund also intends to invest in asset-backed and inflation-protected securities and to engage in dollar rolls on mortgage-related securities. Although the fund may invest in securities of any maturity, the fund’s target dollar-weighted average effective duration, as estimated by the fund’s subadviser, is expected to range between 6 months and 10 years. Effective duration seeks to measure the expected sensitivity of market price to changes in interest rates, taking into account the anticipated effects of structural complexities (for example, some bonds can be prepaid by the issuer). Instead of, and/or in addition to, investing directly in particular securities, the fund may use instruments such as derivatives, including options, interest rate swaps, credit default swaps and options on credit default swaps, futures contracts, and other synthetic instruments that are intended to provide economic exposure to the securities or the issuer or to be used as a hedging technique. The fund may use one or more types of these instruments without limit, subject to applicable regulatory requirements. For additional information regarding derivatives, see “More on the funds’ investment strategies, investments and risks—Derivatives” in the Prospectus. The fund may also engage in a variety of transactions using derivatives in order to change the investment characteristics of its portfolio (such as shortening or lengthening duration) and for other purposes. The fund may borrow money to increase portfolio holdings, to the extent consistent with the fund’s fundamental investment restrictions. The fund is classified as “diversified.”
Western Asset SMASh Series C Fund
Prospectus [Line Items]
Strategy [Heading]	Principal investment strategies
Strategy Narrative [Text Block]	The fund invests in a portfolio of debt obligations of various maturities. Under normal market conditions, the fund expects to invest primarily in corporate obligations and in derivatives and other instruments relating to such investments. The fund currently limits its investments to U.S. dollar denominated investment grade (that is, rated in the Baa/BBB categories or above or, if unrated, determined to be of comparable credit quality by the subadviser) debt obligations. The fund may at times invest in the securities of issuers located in only one country or in a relatively small number of countries, including in any emerging market country or countries. Currently the fund does not contemplate investing 25% or more of its assets in a single country or a small number of countries, except in the United States. The subadviser may invest a significant portion of the fund’s assets in various industry sectors, to the extent consistent with the fund’s fundamental investment restrictions. In purchasing debt obligations for the fund, the subadviser may take full advantage of the entire range of maturities and durations, and may adjust the average maturity or duration of the fund’s investments from time to time. Instead of, and/or in addition to, investing directly in particular securities, the fund may use instruments such as derivatives, including options, interest rate swaps, credit default swaps and options on credit default swaps, futures contracts, and other synthetic instruments that are intended to provide economic exposure to the securities or the issuer or to be used as a hedging technique. The fund may use one or more types of these instruments without limit, subject to applicable regulatory requirements. For additional information regarding derivatives, see “More on the funds’ investment strategies, investments and risks—Derivatives” in the Prospectus. The fund may also engage in a variety of transactions using derivatives in order to change the investment characteristics of its portfolio (such as shortening or lengthening duration) and for other purposes. The fund may borrow money to increase portfolio holdings, to the extent consistent with the fund’s fundamental investment restrictions. The fund is classified as “diversified.”
WESTERN ASSET SMASh SERIES CORE COMPLETION FUND
Prospectus [Line Items]
Strategy [Heading]	Principal investment strategies
Strategy Narrative [Text Block]	The fund has a flexible investment strategy and invests in a variety of securities and instruments and uses a variety of investment techniques in pursuing its objective. The fund presently intends to limit its investments to U.S. dollar denominated securities and currently anticipates that it will generally only purchase debt securities that are rated in the Baa or BBB categories or above at the time of purchase by one or more Nationally Recognized Statistical Rating Organizations (“NRSROs”) or unrated securities of comparable quality at the time of purchase (as determined by the subadviser). These securities are known as “investment grade securities.” The fund may invest a substantial portion of its assets in mortgage-backed and asset-backed securities. Currently the fund does not contemplate investing 25% or more of its assets in a single country or a small number of countries, except in the United States. The fund may invest in issuers located in emerging market countries. The subadviser may invest a significant portion of the fund’s assets in various industry sectors, to the extent consistent with the fund’s fundamental investment restrictions. In purchasing debt obligations for the fund, the subadviser may take full advantage of the entire range of maturities and durations, and may adjust the average maturity or duration of the fund’s investments from time to time. Instead of, and/or in addition to, investing directly in particular securities, the fund may use instruments such as derivatives, including options, interest rate swaps, credit default swaps and options on credit default swaps, futures contracts, and other synthetic instruments that are intended to provide economic exposure to the securities or the issuer or to be used as a hedging technique. The fund may use one or more types of these instruments without limit, subject to applicable regulatory requirements. For additional information regarding derivatives, see “More on the funds’ investment strategies, investments and risks—Derivatives” in the Prospectus. The fund may also engage in a variety of transactions using derivatives in order to change the investment characteristics of its portfolio (such as shortening or lengthening duration) and for other purposes. The fund may borrow money to increase portfolio holdings, to the extent consistent with the fund’s fundamental investment restrictions. The fund is classified as “diversified.”
Western Asset SMASh Series TF Fund
Prospectus [Line Items]
Strategy [Heading]	Principal investment strategies
Strategy Narrative [Text Block]	Under normal circumstances, the fund invests at least 80% of its assets in municipal securities and other investments with similar economic characteristics, the interest on which is exempt from regular federal income tax but which may be subject to the federal alternative minimum tax. The fund’s 80% investment policy may not be changed without shareholder approval. Municipal securities include debt obligations issued by or on behalf of the states, territories and possessions of the United States, and the District of Columbia, and their political subdivisions, agencies and public authorities, and other qualifying issuers. These securities include participation or other interests in municipal securities issued or backed by banks, insurance companies and other financial institutions. Although the fund may invest in securities of any maturity, it normally invests in intermediate-term and long-term municipal securities that have remaining maturities from one to more than thirty years at the time of purchase. The fund typically focuses on investment grade bonds (that is, securities rated in the Baa/BBB categories or above or, if unrated or deemed to be unrated by the subadviser, determined to be of comparable credit quality by the subadviser) but may from time to time invest, to no specified limit, in below investment grade bonds (commonly known as “high yield” or “junk” bonds). Some municipal securities, such as general obligation issues, are backed by the issuer’s taxing authority, while other municipal securities, such as revenue issues, are backed only by revenues from certain facilities or other sources and not by the issuer itself. Instead of, and/or in addition to, investing directly in particular securities, the fund may use instruments such as derivatives, including options, futures contracts and inverse floating rate instruments issued in tender option bond transactions, and other synthetic instruments that are intended to provide economic exposure to the securities or the issuer or to be used as a hedging technique. The fund may use one or more types of these instruments without limit, subject to applicable regulatory requirements. These instruments are taken into account when determining compliance with the fund’s 80% investment policy. For additional information regarding derivatives, see “More on the fund’s investment strategies, investments and risks—Derivatives” in this Prospectus. The fund may also engage in a variety of transactions using derivatives in order to change the investment characteristics of its portfolio (such as shortening or lengthening duration) and for other purposes. The fund may leverage its assets by investing proceeds received through tender option bond transactions, which is considered a form of borrowing. See “More on the fund’s investment strategies, investments and risks—Tender option bonds” in the Prospectus. The fund’s subadviser selects securities to buy and sell for the fund primarily by seeking to identify undervalued sectors and individual securities and securities it believes will benefit from changes in market conditions. It seeks to enhance returns and reduce risks by taking advantage of shifts in the municipal yield curve, credit quality spreads and variations in market sectors. The fund is classified as ”diversified.”
Summary of Definition of Rule 35d-1 Term in Fund Name [Text Block]	Municipal securities include debt obligations issued by or on behalf of the states, territories and possessions of the United States, and the District of Columbia, and their political subdivisions, agencies and public authorities, and other qualifying issuers. These securities include participation or other interests in municipal securities issued or backed by banks, insurance companies and other financial institutions.
Summary of Selection Criteria for Rule 35d-1 Term in Fund Name [Text Block]	Although the fund may invest in securities of any maturity, it normally invests in intermediate-term and long-term municipal securities that have remaining maturities from one to more than thirty years at the time of purchase. The fund typically focuses on investment grade bonds (that is, securities rated in the Baa/BBB categories or above or, if unrated or deemed to be unrated by the subadviser, determined to be of comparable credit quality by the subadviser) but may from time to time invest, to no specified limit, in below investment grade bonds (commonly known as “high yield” or “junk” bonds).
Rule 35d-1 Eighty Percent Investment Policy [Text Block]	Under normal circumstances, the fund invests at least 80% of its assets in municipal securities and other investments with similar economic characteristics, the interest on which is exempt from regular federal income tax but which may be subject to the federal alternative minimum tax. The fund’s 80% investment policy may not be changed without shareholder approval.

Under normal circumstances, the fund expects to invest primarily in a combination of U.S. dollar denominated and non-U.S. dollar denominated investment grade (that is, rated in the Baa/BBB categories or above, or, if unrated, determined to be of comparable credit quality by the subadviser) debt obligations of U.S. and non-U.S. issuers (including emerging market issuers) and in derivatives and other instruments relating to such investments. The fund intends to invest a substantial portion of its assets in mortgage-related securities (including collateralized mortgage obligations), U.S. government securities and money market instruments. The fund also intends to invest in asset-backed and inflation-protected securities and to engage in dollar rolls on mortgage-related securities.

Although the fund may invest in securities of any maturity, the fund’s target dollar-weighted average effective duration, as estimated by the fund’s subadviser, is expected to range between 6 months and 10 years. Effective duration seeks to measure the expected sensitivity of market price to changes in interest rates, taking into account the anticipated effects of structural complexities (for example, some bonds can be prepaid by the issuer).

Instead of, and/or in addition to, investing directly in particular securities, the fund may use instruments such as derivatives, including options, interest rate swaps, credit default swaps and options on credit default swaps, futures contracts, and other synthetic instruments that are intended to provide economic exposure to the securities or the issuer or to be used as a hedging technique. The fund may use one or more types of these instruments without limit, subject to applicable regulatory requirements. For additional information regarding derivatives, see “More on the funds’ investment strategies, investments and risks—Derivatives” in the Prospectus.

The fund may also engage in a variety of transactions using derivatives in order to change the investment characteristics of its portfolio (such as shortening or lengthening duration) and for other purposes.

The fund may borrow money to increase portfolio holdings, to the extent consistent with the fund’s fundamental investment restrictions. The fund is classified as “diversified.”

Prospectus [Line Items]

Strategy Narrative [Text Block]

The fund invests in a portfolio of debt obligations of various maturities. Under normal market conditions, the fund expects to invest primarily in corporate obligations and in derivatives and other instruments relating to such investments. The fund currently limits its investments to U.S. dollar denominated investment grade (that is, rated in the Baa/BBB categories or above or, if unrated, determined to be of comparable credit quality by the subadviser) debt obligations. The fund may at times invest in the securities of issuers located in only one country or in a relatively small number of countries, including in any emerging market country or countries. Currently the fund does not contemplate investing 25% or more of its assets in a single country or a small number of countries, except in the United States. The subadviser may invest a significant portion of the fund’s assets in various industry sectors, to the extent consistent with the fund’s fundamental investment restrictions.

In purchasing debt obligations for the fund, the subadviser may take full advantage of the entire range of maturities and durations, and may adjust the average maturity or duration of the fund’s investments from time to time.

Instead of, and/or in addition to, investing directly in particular securities, the fund may use instruments such as derivatives, including options, interest rate swaps, credit default swaps and options on credit default swaps, futures contracts, and other synthetic instruments that are intended to provide economic exposure to the securities or the issuer or to be used as a hedging technique. The fund may use one or more types of these instruments without limit, subject to applicable regulatory requirements. For additional information regarding derivatives, see “More on the funds’ investment strategies, investments and risks—Derivatives” in the Prospectus.

The fund may also engage in a variety of transactions using derivatives in order to change the investment characteristics of its portfolio (such as shortening or lengthening duration) and for other purposes.

The fund may borrow money to increase portfolio holdings, to the extent consistent with the fund’s fundamental investment restrictions.

The fund is classified as “diversified.”

Prospectus [Line Items]

Strategy Narrative [Text Block]

The fund has a flexible investment strategy and invests in a variety of securities and instruments and uses a variety of investment techniques in pursuing its objective. The fund presently intends to limit its investments to U.S. dollar denominated securities and currently anticipates that it will generally only purchase debt securities that are rated in the Baa or BBB categories or above at the time of purchase by one or more Nationally Recognized Statistical Rating Organizations (“NRSROs”) or unrated securities of comparable quality at the time of purchase (as determined by the subadviser). These securities are known as “investment grade securities.” The fund may invest a substantial portion of its assets in mortgage-backed and asset-backed securities.

Currently the fund does not contemplate investing 25% or more of its assets in a single country or a small number of countries, except in the United States. The fund may invest in issuers located in emerging market countries. The subadviser may invest a significant portion of the fund’s assets in various industry sectors, to the extent consistent with the fund’s fundamental investment restrictions.

In purchasing debt obligations for the fund, the subadviser may take full advantage of the entire range of maturities and durations, and may adjust the average maturity or duration of the fund’s investments from time to time.

Instead of, and/or in addition to, investing directly in particular securities, the fund may use instruments such as derivatives, including options, interest rate swaps, credit default swaps and options on credit default swaps, futures contracts, and other synthetic instruments that are intended to provide economic exposure to the securities or the issuer or to be used as a hedging technique. The fund may use one or more types of these instruments without limit, subject to applicable regulatory requirements. For additional information regarding derivatives, see “More on the funds’ investment strategies, investments and risks—Derivatives” in the Prospectus.

The fund may also engage in a variety of transactions using derivatives in order to change the investment characteristics of its portfolio (such as shortening or lengthening duration) and for other purposes.

The fund may borrow money to increase portfolio holdings, to the extent consistent with the fund’s fundamental investment restrictions. The fund is classified as “diversified.”

Prospectus [Line Items]

Strategy Narrative [Text Block]

Under normal circumstances, the fund invests at least 80% of its assets in municipal securities and other investments with similar economic characteristics, the interest on which is exempt from regular federal income tax but which may be subject to the federal alternative minimum tax. The fund’s 80% investment policy may not be changed without shareholder approval.

Municipal securities include debt obligations issued by or on behalf of the states, territories and possessions of the United States, and the District of Columbia, and their political subdivisions, agencies and public authorities, and other qualifying issuers. These securities include participation or other interests in municipal securities issued or backed by banks, insurance companies and other financial institutions.

Although the fund may invest in securities of any maturity, it normally invests in intermediate-term and long-term municipal securities that have remaining maturities from one to more than thirty years at the time of purchase. The fund typically focuses on investment grade bonds (that is, securities rated in the Baa/BBB categories or above or, if unrated or deemed to be unrated by the subadviser, determined to be of comparable credit quality by the subadviser) but may from time to time invest, to no specified limit, in below investment grade bonds (commonly known as “high yield” or “junk” bonds).

Some municipal securities, such as general obligation issues, are backed by the issuer’s taxing authority, while other municipal securities, such as revenue issues, are backed only by revenues from certain facilities or other sources and not by the issuer itself.

Instead of, and/or in addition to, investing directly in particular securities, the fund may use instruments such as derivatives, including options, futures contracts and inverse floating rate instruments issued in tender option bond transactions, and other synthetic instruments that are intended to provide economic exposure to the securities or the issuer or to be used as a hedging technique. The fund may use one or more types of these instruments without limit, subject to applicable regulatory requirements. These instruments are taken into account when determining compliance with the fund’s 80% investment policy. For additional information regarding derivatives, see “More on the fund’s investment strategies, investments and risks—Derivatives” in this Prospectus.

The fund may also engage in a variety of transactions using derivatives in order to change the investment characteristics of its portfolio (such as shortening or lengthening duration) and for other purposes. The fund may leverage its assets by investing proceeds received through tender option bond transactions, which is considered a form of borrowing. See “More on the fund’s investment strategies, investments and risks—Tender option bonds” in the Prospectus.

The fund’s subadviser selects securities to buy and sell for the fund primarily by seeking to identify undervalued sectors and individual securities and securities it believes will benefit from changes in market conditions. It seeks to enhance returns and reduce risks by taking advantage of shifts in the municipal yield curve, credit quality spreads and variations in market sectors.

The fund is classified as ”diversified.”

Summary of Selection Criteria for Rule 35d-1 Term in Fund Name [Text Block]

Although the fund may invest in securities of any maturity, it normally invests in intermediate-term and long-term municipal securities that have remaining maturities from one to more than thirty years at the time of purchase. The fund typically focuses on investment grade bonds (that is, securities rated in the Baa/BBB categories or above or, if unrated or deemed to be unrated by the subadviser, determined to be of comparable credit quality by the subadviser) but may from time to time invest, to no specified limit, in below investment grade bonds (commonly known as “high yield” or “junk” bonds).